A hand held radiation detector is disclosed in U.S. patent application Ser. No. 466,789, now U.S. Pat. No. 4,566,808, by Pompei and Daya. That radiation detector is a flat package having a radiation sensor at one end thereof and a bar graph display at the other end. The bar graph display has a quick response such that an area of interest can be scanned with the radiation sensor while the user of the instrument observes the bar graph. High and low levels of radiation within a scan are readily observed on the bar graph and differentials between the high and low regions are quickly obtained.
The detector has a field of view of about 12 degrees. The ratio of the viewing distance to the diameter of the viewed spot was approximately 5 to 1. Such a unit is particularly suited to scanning surfaces or devices at close to medium ranges of up to about 10 feet. For many applications, beyond about 10 feet the area viewed by the detector becomes large relative to the subject of interest. For example, when scanning an electrical line connection about 100 feet high on a pole, heat radiation from the connection is washed out by the background viewed by the detector because the connection is only a small portion of the overall field of view. Therefore, for such applications it would be desirable to have a unit having a smaller field of view such as about 1 or 2 degrees.